The order Ascoceratida is reviewed in relation to recent contributions to the literature, and evolution of the group is outlined. New forms include Montyoceras tuba, Redpathoceras clarki, new species of Probillingsites: obstusus, globosus, sinuatus, minor, and epiphaniensis. Review of Schuchertoceras and Billingsites indicated merging the genera for practical reasons; new Billingsites species are shideleri, subconicus, and ovalis. The new genus Redpathoceras supplies a link, both in age and in form, between the Chazyan Hebetoceratinae and the Trenton to Richmond Probillingsites. New material adds to the knowledge of the internal structure of Probillingsites. Amphoreopsis Creek, restudied as a possible ascoceroid, is doubtfully distinct from Poterioceras, and its supposed muscle impressions are adventitious.